Circuit breaker



June 16, 1936. l H. D. DORFMAN ETAL. 2,()44157 CIRCUIT BREAKER Filed July 20, 1935 f: 75 /7 A@ z/ 95 g 7 35 7? 77 wlTNEssEs; lNvENToRs Patented June 16, 1936 CIRCUIT BREAKER 'Hiller D. Dorfman and John H. Shuler, Mansfield, Ohio, assignors .to Westinghouse Electric & vManufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 20, 1933, Serial No. 681,300 A14 claims. (c1. 20o-113) Our invention relates to circuit"breakers and particularly to circuit breaker trip devices which utilize a. thermally responsive bimetallic tripl member.

One object of our invention is to provide an improved bimetallic trip member for use in conjunction with circuit breakers wherein accuracy of response to abnormal circuit conditions and permanency of calibration are paramount requirements.

Another object of our invention is to provide means for increasing the thermal capacity of a bimetallic trip element without affecting the overall electrical resistance in order to prevent the excessive heating which results during the occurrence of short circuit or heavy overload conditions from injuring the trip element.

A further object of our invention is to provide a current carrying bimetallic trip element wherein the area of greatest heating shall be confined to that portion of the elementvwhere excessive temperatures are least apt to aiiect the calibration of the element.

A still further object of our invention is to provide a bimetallic trip element that shall operate with a greater time delay without danger of disturbing the calibration of the element than has been heretofore possible.

The principal iield for immediate application of our invention is in connection with trip devices for snap-acting circuit breakers such as are used for controlling lighting and distribution feeder circuits. Circuit breakers of this type are subject to very severe operating conditions,

' due to the large amounts of power ordinarily available in the supply circuits, and at the same time, the breakers must, be capable of quickly and effectively interrupting the controlled circuit upon the occurrence of predetermined overload conditions. The trip elements must be of sulcient thermal capacity to prevent any change in their calibration during the circuit interrupting operation, and while accuracy of operation upon the occurrence of continuing overloads of predetermined magnitude is highly important, there must be no interruption of the circuit upon the occurrence of slight or transient overloads.

These requirements have not been satisfactorily met by the bimetallic trip elements heretofore known to the art. lThe previously known bimetallic elements which possessed the desired time characteristic were incapable of retaining their calibration during the interruption of large magnitude overloads, the arc persisting for a sunicient period of time to heat portions of the element to a temperature at which a permanent set was effected. This, of course, destroyed the calibration of the element, and constituted a serious danger to the apparatus protected by the breaker upon the occurrence of subsequent overloads. Other bimetallic trip elements were satisfactory from the viewpoint ofl permanency of calibration but possessed an unsatisfactory time characteristic.

Our invention, however, possesses the desirable characteristic of substantial permanence of calibration under present day operating conditions and, in addition, is capable of accurately distinguishing between transient overloads and continuing overloads, so as to prevent annoying interruptions of service while giving yadequate protection to the controlled apparatus at all times.

In the preferred embodiment of our invention, we provide a manually operable mechanism for moving a switch member to the open or closed position, a stationary contact member for cooperating with the movable switch member, an insulating base for mounting the various elements of the circuit breaker, an arc extinguishing device fixed to the base adjacent the path of movement of the movable switch member, a means for biasing the switch member to the open position, a releasable restraining means for holding the switch member in the closedl position, and a trip device including a bimetallic trip element for engaging and releasably restraining the means holding the switch member in the closed position.

The-features of ourinvention which we believe to be new are particularly pointed out in the appended claims, and for a full understanding of the principles of the invention, reference may be had to the accompanying drawing in which:

Figure 1 is a view, partially in section and partially in side elevation, of a circuit breaker embodying the principal elements of our invention;

Fig. 2 is a front elevational view showing a trip device of the circuit breaker illustrated in Fig. 1;

Fig. 3 is a side elevational view oi the trip device shown in Fig. 2;

Fig. 4 is a front elevational view of the bimetallic trip element forming a part of the trip device shown in Figs. 2 and 3; and

Fig. 5 is a side elevational view of the bimetallic trip element shown in Fig. 4.

Referring to the drawing, the base I of the .circuit breaker is of molded insulating material and has mounted thereon the terminal contacts 3 and 5. the trip device 1, the circuit breaker operating mechanism 9 which has associated therewith the switch member II, the arc extinguisherlIS, and the main stationary contact I5. A cover (not shown) of molded insulating material is ordinarily provided for enclosing and protecting the mechanism of the circuit breaker. An operating handle I 1, also of molded insulating material, is provided for actuating the operating mechanism 9. The trip device 1 is supported on the base I and positioned with respect to the operating mechanism by means of suitable screws I9 which engage threaded inserts 2I molded in the base. These screws I9 also serve to connect the trip device 1 in the electric circuit. 'I'he operating mechanism 9 and the arc extinguisher I3 are aflixed to the base I by means of screws 23 which extend through suitable openings 25 therein.

The electrical circuit through the breaker is very direct; beginning with the terminal contact 3, the current flows successively through the conducting strip 21, the stationary contact I5, the moving Contact which is supported on the resilient switch arm 3|, the flexible conducting shunt 33 which is electrically connected to one terminal of the trip device 1 by means of one of the screws i9, thence through the U-shaped bimetallic trip element 35 and the other conducting strip 31 to the second terminal contact The structural details of the circuit breaker operating mechanism 9 and the arc extinguisher i3 are not important parts in this invention, and any suitable mechanism which is adapted t0 engage a trip latch may be used. We prefer, however, to utilize a mechanism similar to that disclosed in the application of H. D. Dorfman, Serial No. 600.660, led on March 23, 1932, and assigned to the assignee of this invention. A somewhat similar mechanism is also shown in Patent No. 1,802,758.

The switch ,member II has a channel shaped frame 39 which is pivotally supported on to the U-shaped frame 4I of the circuit breaker operating mechanism 9 through the agency of a pivot pin 43. The resilient switch arrn 3I is preferably constructed of spring steel, and, as previously pointed out, the moving contact 29 is rigidly affixed to the free end thereof by means of a rivet 45. The switch arm itself is aixed to the channel shaped frame by means of two other rivets 4l. The flexible conducting shunt 33 is electrically connected to-the moving contact 29 at one end and is provided with a terminal 49 at the other end adapted to be held in place by one of the screws i9. Round spacing washers 5I are provided to position the switch member frame 39 between the upstanding sides of the frame 4I of the operating mechanism S.

We prefer to use arc resisting material for both the moving and the stationary contacts, the former being composed of finely divided silver and graphite compressed into a conglomerate mass, and the latter being composed of a silver n10- lybdenum alloy.

The arc extinguisher I3 is preferably oi the spaced plate type in which a plurality of slotted plates of magnetic material each insulated from the adjacent plates and having a slot therein are provided. The slots in the plates are of substantially the same outline as the moving contact and the extinguisher is positioned closely adjacent the arc path. The magnetic plates so alter the iield adjacent the are that it is moved into the spaces therebetween/where it is quickly cooled and extinguished.

In the structure shown in Fig. 1 the magnetic plates 53 having slots 55 therein are assembled between two end plates 51 of insulating material, projecting lugs (not shown) being provided in the magnetic plates for engaging the end plates.

The operating mechanism 9 comprises in general a U-shaped base 4I, a pair of toggle links 59 and 6I for engaging and actuating the frame 39 of the switch member' II, a releasable carrier 53 for restraining the toggle links in an operative position, an operating member I1, and a pair of over-center springs for connecting the operating member I1 to the knee oi' the toggle links. The U-shaped base 4I, as previously pointed out, is fastened to the insulating base I of the circuit breaker proper by means of two screws 23 that engage suitable threaded openings therein. The pivot pin 43 which provides a pivot point for the switch member II extends through aligned openings in the opposite sides of the U. Other openings are provided for the reception of the pivot pins 61, one on either side of the U, which provide pivot points for the bifurcated portion 69 of the operating member.

The lower end (with respect to the base) of the toggle link 6I is pivoted to the frame 39 of the switch member I I by means of a pivot pin 1I. The upper end of the toggle link 6I is pivoted to one end of the second toggle link 59 by means of the knee pivot `pin 13. One of the operating springs 55 engages each end of the knee pivot pin i3 and thus serves to operatively connect the knee of the toggle with the operating member I1. 5

Thecarrier 63 which is pivoted about the pin 15 provides a releasable restraining means for holding the toggle links in an operative position, the upper end of the toggle link 59 being pivotally fastened to the carrier through the agency of a pin 11. The movement of the carrier about its pivot pin 15 in a clockwise direction is limited by the projection 'i8 which extends inwardly from one side of the U-shaped base 4I. The limits of motion of the bifurcated portion 69 of the operating member i1 are defined by the offset projections 3i and 83 forming a part of the sides of the U-shaped base 4i. The carrier is provided with a projecting portion 85 adapted to engage the trip device.

The trip device 1 includes a current-carrying bimetallic trip element 35, a latch plate 81 which is mechanically fastened to the upper end of the bimetallic trip element 35 but is electrically insulated therefrom by means of two mica plates 89, the latch plate 81 being held in position by two rivets 9i which extend through a retaining plate 33 and enlarged openings :'35 in the top portion of the bimetallic trip element itself.

As shown particularly in Fig. l, the trip device is supported upon its own terminal 31 through the agency of the screws i9 which also serve to complete the electrical circuit. lThe bimetallic element 35, as shown particularly in Figs. 2 to 5 inclusive, comprises a U-shaped member of bixnetallic material which is provided with two circular openings 95 in its free end, a plurality oi equally spaced fins or lugs 99 along the sides of the U, and a pair of terminal or foot portions 91 integral with the bimetallic element and projecting outwardly therefrom at an angle substantially equal to 90. purpose of increasingthe thermal capacity of the bimetallic element 35 without affecting its electrical resistance to any great degree. Ex-

The fins 39 are provided for the Cil periments indicate Athat the provision of fins, such as thosey illustrated in Figs. 2 to 5 inclusive, increase the thermal capacity of a U-shaped current carrying bimetallic trip element approximately 15%, it being believed by applicants that this increase is practically entirely due to the increased area of radiation.

It will be noted, upon inspection of the blmetallic element illustrated in Fig. 4, that the cross-sectional area of the current path in the region adjacent the openings 35 is considerably less than the mean cross-sectional area in any other part of the U. This means that the maximum resistance per increment of length exists in the region adjacent these openings. In other words, the maximum heating is confined to the freely movable top portion of the bimetallic trip element. At the same time, this reduction in the cross-sectional area of the current-carrying pai increases the overall resistance and makes possible the inclusion of a greater mass of material in the lower portions of the element, thereby increasing the thermal capacity of the trip device.

The localizing of the area of maximum heating has several other advantages. It makes possible the securing of a considerably greater time delay than is possible in a trip element which utilizes a current carrying path of substantially uniform cross-sectional area, because of the time required for the heat to reach that part of the element which is most effective in causing deflection--the restrained portion, and, in addition, by confining the area of maximum heating to that portion of the bimetallic element which is least effective in securing deflection of the trip element, it obviates, to a great degree, any possibility of danger to the calibration of the trip device. This obviously follows from the fact that a permanent deformation in the freely movable end of the bimetallic element will have very little effect on the subsequent deflection of the element for a given current. The danger of possible deformation isv further lessened since the latch plate 81 and its associated retaining means tend to prevent any deformation even in the free end, due to the fact that the plates serve as a strengthening means for the bimetallic element.

The carrier member 63 is at all times biased in a clockwise direction (Fig. 1) by the reaction force of the over-center springs B5. This force must be balanced by the trip device 1 and result in the placing ofthe bimetallic element 35 under a tensional stress when the circuit breaker mechanism is in the untripped condition.

The circuit breaker is shown in the closed position in Fig. l, and it will be noted that the knee of the toggle has been moved to the over-center, or latched position. To open the contacts manually the operating handle I1 is moved in the counter-clockwise direction about its pivot point (the pins 61); shortly before the operating handle I1 has reached its limit of travel in the counter-clockwise direction the line of action in-the over-center springs 65 is brought to the left of the center line of the toggle. This results in the producing of a component of force which moves the toggle to the collapsed position. Since movement of the knee of the toggle from the position shown in Fig. 1 toward the collapsed position results in a progressive increasing of the force causing the movement, the opening operation once started takes place automatically and results in the separation of the contacts with a snap action.

The closing operation is substantially the reverse of the opening operation. The handle I1 is moved in a clockwise direction, the resulting tension of the over-center springs 65 causes the knee of the toggle to move toward the closed cir- Aelement to deflect away from the operating mechanism 9. If the overload persists for a sumcient interval of time, this deflection becomes great enough to move the latch plate 81 out of engagement with the end 85 of the carrier 33. This unlatching or releasing of the carrier B3 allows that member to move freely in a clockwise direction about its pivot pin 13 under the influence of the reaction forces of the over-center springs 6 5. Almost immediately the end of the toggle link 59whicll is pivoted on the carrier is moved a sufficient distance to the right of the centerline of the toggle to cause the toggle to collapse as a result of the tension force applied to the knee pivot pin 13 by the overcenter springs 65. The switch member frame 39 rotates about its pivot pin 43 and moves the contact to the open circuit position in exactly the same manner as described for manual operation.

Following the tripping operation and the resulting change in position of the knee pivot pin 13, the operating handle I1 is biased in a counterclockwise direction but moves only to the middle position, due to the engagement of the downwardly projecting member 10| with the end |03 of the cradle 63. This movement of the handle I1 to the mid-position following the tripping of the breaker serves as a ready indicating means for showing that the circuit has been opened in response to an abnormal electrical condition.

During the tripping operation. the movement of the bimetallic member 35 does not occur simultaneously with the occurrence of the overload, 4

nor does it occur simultaneously with its own heating, due to the mechanical inability of metal to expand instantaneously. Further, the heating continues after the trip device has been actuated, vdue to the time required to extinguish the arc, and if any external force acts on the bimetallic element during the time of aro extinction that element, due to its high temperature, may take on a permanent set. In fact, unless some provision is made for taking care of the heating during this period of arc extinction the permanent set may result even when the bimetallic element is unstres'sed. Of course, if this occurs the calibration is entirely destroyed and serious damage may result to the equipment which is protected thereby upon the occurrence oi' subsequent overload conditions. The trip device disclosed in this embodiment of our invention is so designed that the bimetal is freed from external stress immediately following the opening of the 65 breaker contacts, and as previously pointed out, is of such design that heating sufficient to cause a permanent set is unlikely to occur, and, if it does occur, it is restricted to that portion of the element which least effects the calibration.

The entire mechanism is entirely resettable by movement of the operating handle l1 as soon as the bimetallic trip element 35, has cooled sumciently to restore the latch plate 81 to the position shown in Fig. 1.

As mentioned above, the

projection IUI which extends downwardly from the operating handle I1 engages the end |03 of the cradle 63 when the breaker is in the tripped position. To reset the mechanism, the handlel I1 is moved to the full oil position. This movement causes a rotation of the cradle 63 in a counter-clockwise direction about its pivot pin 15, the end of the cradle engages the top of the latch plate 81, moves that member and with it the entire trip device so as to permit the reengagement of the end of the cradle beneath the latch plate by the time the handle has reached the full off position. The breaker may then be closed manually as described in the previous paragraph.

. The operating mechanism 9 is trip free of the operating handle Il because the movement of the cradle 63, following its release by the trip latch is independent of the position of the handle il, and because the parts are so proportioned that the toggle cannot be held from collapsing following the release of the cradle.

It is, of course, conceivable and within the scope of our invention that an external heater could be used in conjunction with a bimetallic trip element to secure the local heating at one end, now made possible by the openings 95. This arrangement would, however, be more expensive than the structure we have disclosed and might not have quite as satisfactory operating characteristics.

It will thus be seen that we have disclosed an improved circuit breaker trip device utilizing a current carrying bimetallic element which is capable of being used in circuits handling large amounts of power Without danger of losing its calibration. In addition, we have disclosed'how this trip clement may be utilized in a circuit breaker having means associated therewith for removing all stress from the .bimetallic element during that period of time when permanent cleformation is apt to occur.

While, in accordance with the patent statutes, we have given the foregoing details of a practical embodiment of our invention, it is to be understood that many of these details are merely illustrative and that variations in their precise form will be desirable in some applications. We desire, therefore, that the language of the accompanying claims shall be accorded the broad est reasonable construction, and that our invention be limited only by what is explicitly stated in the claims and by the prior art.

We claim as our invention:

l. In electrical apparatus, a current carrying electro-responsive element, at least a considerable portion of the current carrying path oi which comprises means of bimetallic material having a plurality of spaced, outwardly projecting ns, formed integral therewith, for increasing the thermal capacity of said element.

2. In electrical apparatus, a thermally responsive device having a pair of leg portions, and conducting means for connecting said leg portions at one end thereof, at least one of said leg portions being of bimetallic material and having a plurality of spaced, outwardly projecting ns for increasing the thermal capacity of said device,

3. In electrical apparatus, an electro-responsive device comprising a substantially U-shaped member of bimetallic material, the leg portions of which have a plurality of spaced, outwardly projecting fins formed integral therewith for increasing the thermal capacity of said member.

4. In electrical apparatus, .a current conducting, thermally-responsive element comprising a flat, looped member formed of sheet bimetalllc material, said member having a substantially uniform electrical resistance per unit of length along the current carrying path thereof except adjacent the closed end of said loop, the electrical resistance of the portion adjacent the closed end of said loop being considerably greater per unit of length than said substantially uniform resistance.

5. In electrical apparatus, a current conducting, thermally-responsive element comprising a flat, substantially U-shaped member formed of sheet bimetallic material, said member having a substantially uniform electrical resistance per unit of length along the current carrying path thereof except adjacent the closed end of said U, the electrical resistance for the portion adjacent the closed end o1 said U being considerably greater per unit of length than said substantially uniform resistance.

6. In electrical apparatus, a current conducting, thermally-responsive element comprising a flat, looped member formed of sheet bimetallic material, said member having a substantially uniform electrical resistance per unit of length along the current carrying path thereof except adjacent the closed end of said loop, the electrical resistance for the portion adjacent the closed end of said loop being considerably greater per unit of length than said substantially uniform resistance, the leg portions of said loop having a plurality of outwardly projecting portions, spaced therealong at substantially regular intervals for increasing the thermal capacity of said 5 element.

7. In electrical apparatus, a current carrying, electro-responsive element comprising a at strip of conducting material, at least a portion of said strip being of thermally responsive material, means for restricting the effective width of the major portion of the current carrying path through said strip to a width appreciably less than the maximum width of said strip.

8. In electrical apparatus, a current carrying i;

electro-responsive element, at least a considerable portion of the current carrying path of which comprises means of bimetallic material, a sub-- stantial portion of the edges of said element being serrated in order to increase the thermal capacity of said element.

9. In electrical apparatus, a thermally responsive device having a pair of leg portions, and conducting means-for connecting said leg portions at one end thereof, at least one of said leg portions comprising a strip of bimetallic material of substantially uniform Width, at least one of the edges of said strip of bimetallic material being serrated in order to increase the thermal capacity of said device.

l0. In electrical apparatus, an electro-responsive device comprising a substantially U-shaped member of bimetallic material, the leg portions of said member being of substantially imiform width and having serrated edges in order to increase the thermal capacity of said member.

ll. In electrical apparatus, an electro-responsive device comprising a substantially U-shaped member formed from a fiat sheet of bimetallic material, at least one of the leg portions of said member being serrated in order to increase the thermal capacity of said member.

l2. In electrical apparatus, la current-carrying electroresponsive device comprising a substantially U-shaped member of bimetallic material, 75

means for supporting said member adjacent the open end of said U, the closed end of said U being movable to actuate said apparatus, at least one of the side portions of said U being serrated in order to increase the thermal capacity of said device, and means whereby the cross-sectional area of the current-carrying path through said strip is minimized adjacent said movable end.

13. In electrical apparatus, a current-carrying electroresponsive device comprising a substantially U-shaped member formed from a iiat sheet of bimetallic material, means for supporting said member adjacent the open end oi' said U, the closed end of said U being movable to actuate said apparatus, the leg portions of said member being serrated in order to increase the thermal capacity of said device, and means including a cut-out portion disposed adjacent the closed end. of said member for locally decreasing the crossof said device.

sectional area of the current path through said element.

14. In electrical apparatus, a current-carrying thermally-responsive device comprising a flat substantially U-shaped member formed from sheet bimetallic material, means for supporting said member adjacent the open end of said U, the closed end of said U being movable when said, member is heated to actuate said apparatus, and means for heating said member consisting of means for connecting said member into an electrical circuit, the closed end of said U having a cut-out portion therein in order that the heating of said member produced by the ow of electrical current therethrough shall be greatest adjacent said movable end at all times during the operation HILLER D. DORFMAN. JOHN H. SHULER. 

